This disclosure relates generally to patient monitoring. More particularly, the present invention relates to patient monitoring and monitors, in which several physiological parameters are derived from a subject and various signal information, such as the time evolutions of the parameters, may be presented to the user. The physiological signal data involved may be, for example, EEG signal data.
Patient monitors are electronic devices designed to display physiological information about a subject. Electrocardiogram (ECG), electroencephalogram (EEG), plethysmographic signals, and signals related to blood pressure, temperature, and respiration represent typical physiological information contained in full-size patient monitors. A patient monitor may also be designed to display physiological information from one organ only; a full-size EEG monitor, for example, may display EEG signal information from even 64 measurement channels. The EEG monitors currently used in neurological and intensive care monitoring are either integrated full-size patient monitors or devices specifically designed to monitor EEG information only. Depending on the application, EEG monitors typically employ EEG signals measured from 4 to 32 measurement channels. The monitors derive several different variables or parameters from each of the measurement channels. For example, 8 EEG parameters may be derived from each measurement channel, whereby the total number of EEG parameters is between 32 and 256, depending on the number of the measurement channels. In addition, more EEG signals may be derived from the measured data by simple subtraction operations. For example, by subtracting the EEG signals of two measurement channels a new EEG signal representing the voltage difference between two measurement points is obtained. This possibility may vastly increase the amount of information obtained. The time evolutions of the parameters are typically displayed in trend-graphs, where time is displayed in the x-axis and the corresponding parameter value in the y-axis. The time axis shown is normally rather wide, between 2 and 48 hours.
Due to the limited size of the display of the monitor, all the information acquired from a subject cannot be displayed to the user at one time but the user must select the information to be displayed at each time through the user interface of the monitor. The information that is visible at one time on the screen of the display is in this context termed a screen page. The information that may be displayed to the user is thus divided between a plurality of screen pages. One of the screen pages is typically the default screen page and it includes information that is regarded as the most vital in view of the state of the subject. The default screen page is here termed the primary screen page, while the other screen pages that may be selected by the user are termed secondary screen pages. Various trend-graphs are typically displayed on the secondary screen pages and the user interface of the patient monitor is provided with tools, such as a menu system and/or a switch knob, for changing the screen page to be displayed at each time.
Consequently, the user has to browse the screen pages to find the information of his/her interest. The high amount of information included in the trend-graphs may, however, delay clinical decision-making, since the user has to browse several screen pages and since the monitor cannot assist the user for speeding up the discovery of the information that may be relevant at each time and before any limits of the alarming functionality are exceeded.
This drawback is further aggravated by the fact that part of the information related to the trend-graphs may be irrelevant, because some parameters are useful only within a specific etiology group of patients. Therefore, the user may have to find the relevant information from among information that may be more or less irrelevant. In addition, the selection of relevant information is slowed down by the fact that some parameters are affected only in rare occasions and remain unchanged most of the time.
Patient monitors are typically also furnished with the above-mentioned alarming functionality. Alarms are normally both audible and visual effects aiming to alert the nursing staff to a life-threatening condition or to another event considered vital. For example, a patient monitor alarms if arterial blood oxygen saturation drops below 90%. In most monitors, the alarm limits may be defined by the user, since the limits typically depend on patient etiology, age, gender, medication, and various other subjective factors. For example, upper limits for heart rate, indicating tachycardia, are higher in infants and children than in adults.
Various clinical decision support systems may also used to assist the physicians and the nursing staff in clinical decision-making. However, the use of fixed alarm limits or decision support systems cannot assist a clinician in detecting the less critical physiological changes and trends that may, in the course of time, lead to a life-threatening condition or to another vital change in the state of the patient. Furthermore, clinical decision support systems are complex and expensive, due to the embedded diagnostic intelligence.